Kristen Nicholas has similar patterns and offers a kit for her Circles Sampler Pillow with everything needed to make an 18" x 18" pillow except the hoop, backing fabric and piping, and the pillow form. If you don't like the turquoise fabric, you just need to let her know what colour you would prefer and she'll send it instead. For $46US, it's a good deal. You can't buy a finished designer pillow for that.
After watching numerous videos on creating a pillow cover, I made one yesterday.
The piping is first attached to the front of the pillow with raw edges matching. I then installed a lapped zipper on the back and trimmed the back to match the front. (I didn't get a shot of the flat backing piece with the zipper installed).
I could have used an invisible zipper but I thought that would be a bit difficult getting it to butt against the piping. It was really easy to just lap the larger piece over the smaller piece that had one side of the zipper attached. This video was really helpful outlining the steps for installing the zipper. The full video covering all the steps for making a pillow cover is here.
I stuffed the pillow form in,
Making and adding the piping was really easy. I'm glad I 'went for it' and got the pillow finished.